1. Field of the Invention
The present invention relates to a signal processing method and apparatus for recording a digital signal in a recording medium or for transmitting to a transmission medium, a signal reproducing method and apparatus for reproducing the digital signal recorded in the recording medium or transmitted via the transmission medium, and further a recording medium in which the digital signal is recorded.
2. Description of the Related Art
Recently, any type of information can be digitized and technology capable of distributing such information through transmission media or recording media has been developed, as expressed by the term “digital revolution.” As a result, a great number of people have come to acquire digital information freely. In such an environment, signals such as digital audio signals, digital video signals, relating data which computers handle are recorded in a recording medium. Information transmission and storage are carried out so that the above-described signals are reproduced from the recording medium, information is copied to a read-only medium, transmitted information is reproduced or information is transmitted through a transmission line.
Recently, as a recording medium capable of recording a large volume of video/audio information, the digital versatile disc (DVD) has been realized. A movie over two hours long is recorded in a DVD and such DVD recorded information is reproduced through a playback apparatus, so that the movie can be watched freely at home.
DVDs are classified into: read-only DVD-ROMs, DVD-Rs which allow a one-time recording, and DVD-RW, DVD-RAM which allow re-recording.
An application standard for DVD-ROM includes a DVD-video standard which allows a whole movie to be recorded in a single disc. A user can acquire information based on digital signals freely through reproduction of such DVD-video discs or reception of digital broadcasting. Under such circumstances, if the acquired digital signals are copied to a recording medium such as a hard disc and the aforementioned DVD-RAM and encoded with an encoder based on the DVD-video standard, it is possible to copy a disc.
Thus, in a DVD-video, digital information to be recorded is encrypted. The copy protect method employing cryptography technology functions effectively for a DVD-video disc or DVD-ROM, in which encrypted information is pre-recorded.
Examples of a conventional technique relating to encryption include a technique described in Jpn. Pat. Appln. KOKAI Publication No. 11-86436. In this technique, specific data different from main information data is mixed in an error correction code block. The specific data is used as copy inhibition information. Another example is a technique described in Jpn. Pat. Appln. KOKAI Publication No. 9-128890. In this technique, in order to prevent illegal copy of the digital signal, a part of an error correction code is replaced with specific data (such as an encryption key) and recorded. Further example is a technique described in Jpn. Pat. Appln. KOKAI Publication No. 8-204584. In this technique, in a case in which data subjected to an error correction processing is supplied to a decryption processing block, an uncorrectable data portion is changed to a special code including a synchronous code and transmitted so that the portion can be detected by a decryption processing section. An error portion is recognized by using the special code, and decryption is performed based on the error portion.
In a field in which the above-described information/storage processing is performed, it has further become important, in recent years, to handle copyright protection. Particularly, when the information requiring the copyright protection is recorded in a conventional recording medium, illegal copying needs to be prevented. That is, although a copyright holder permits information recording only for one recording medium, the same information may be recorded in a plurality of recording media. As a result, and it is absolutely necessary to prevent illegal copying. Moreover, there has been a demand for further reinforcement in the prevention of illegal copying.